There are many previous patents and prior art devices which attempt to provide point of operation safety to protect the operator from the pinch point. However, these attempts have shown to be costly, cumbersome, inefficient and, most importantly, they are not tamper-proof and can reduce either the effectiveness or the operating speed of the machine.
For example, the prior U.S. Pat. No. 4,395,641 to Dise shows a point of operation safety device which employs an external sensing probe to predetermine a safe condition around the workpiece to control operation of the machine. This probe, however, adds an additional complexity to the machine and presents an obstruction in the area at the point of operation which hinders the free and efficient use of the machine.
U.S. Pat. No. 4,570,839 to Cox et al discloses a press with simple contact switches to limit the high force portion of the ram stroke to a small range near the work- piece.
Likewise, other machines have employed various sensing devices for establishing a safety condition as a limit for machine operation. However, all of these safety devices have some of the problems mentioned above including the fact that these extra mechanisms may be easily deactivated or dismantled by owners or the operators in order to increase production speed at the sacrifice of operator safety.